docs: def Bankoff(m, x, rhol, rhog, mul, mug, D, roughness=0, L=1):
      r'''Calculates two-phase pressure drop with the Bankoff (1960) correlation,
      as shown in [2]_, [3]_, and [4]_.
  
      .. math::
          \Delta P_{tp} = \phi_{l}^{7/4} \Delta P_{l}
  
      .. math::
          \phi_l = \frac{1}{1-x}\left[1 - \gamma\left(1 - \frac{\rho_g}{\rho_l}
          \right)\right]^{3/7}\left[1 + x\left(\frac{\rho_l}{\rho_g} - 1\right)
          \right]
  
      .. math::
          \gamma = \frac{0.71 + 2.35\left(\frac{\rho_g}{\rho_l}\right)}
          {1 + \frac{1-x}{x} \cdot \frac{\rho_g}{\rho_l}}
  
      Parameters
      ----------
      m : float
          Mass flow rate of fluid, [kg/s]
      x : float
          Quality of fluid, [-]
      rhol : float
          Liquid density, [kg/m^3]
      rhog : float
          Gas density, [kg/m^3]
      mul : float
          Viscosity of liquid, [Pa*s]
      mug : float
          Viscosity of gas, [Pa*s]
      D : float
          Diameter of pipe, [m]
      roughness : float, optional
          Roughness of pipe for use in calculating friction factor, [m]
      L : float, optional
          Length of pipe, [m]
  
      Returns
      -------
      dP : float
          Pressure drop of the two-phase flow, [Pa]
  
      Notes
      -----
      This correlation is not actually shown in [1]_. Its origin is unknown.
      The author recommends against using this.
  
      Examples
      --------
      >>> Bankoff(m=0.6, x=0.1, rhol=915., rhog=2.67, mul=180E-6, mug=14E-6,
      ... D=0.05, roughness=0, L=1)
      4746.059442453399
  
      References
      ----------
      .. [1] Bankoff, S. G. "A Variable Density Single-Fluid Model for Two-Phase
         Flow With Particular Reference to Steam-Water Flow." Journal of Heat
         Transfer 82, no. 4 (November 1, 1960): 265-72. doi:10.1115/1.3679930.
      .. [2] Thome, John R. "Engineering Data Book III." Wolverine Tube Inc
         (2004). http://www.wlv.com/heat-transfer-databook/
      .. [3] Moreno Quibén, Jesús. "Experimental and Analytical Study of Two-
         Phase Pressure Drops during Evaporation in Horizontal Tubes," 2005.
         doi:10.5075/epfl-thesis-3337.
      .. [4] Mekisso, Henock Mateos. "Comparison of Frictional Pressure Drop
         Correlations for Isothermal Two-Phase Horizontal Flow." Thesis, Oklahoma
         State University, 2013. https://shareok.org/handle/11244/11109.
      '''
      # Liquid-only properties, for calculation of dP_lo
      v_lo = m/rhol/(pi/4*D**2)
      Re_lo = Reynolds(V=v_lo, rho=rhol, mu=mul, D=D)
      fd_lo = friction_factor(Re=Re_lo, eD=roughness/D)
      dP_lo = fd_lo*L/D*(0.5*rhol*v_lo**2)
  
      gamma = (0.71 + 2.35*rhog/rhol)/(1. + (1.-x)/x*rhog/rhol)
      phi_Bf = 1./(1.-x)*(1 - gamma*(1 - rhog/rhol))**(3/7.)*(1. + x*(rhol/rhog -1.))
      return dP_lo*phi_Bf**(7/4.)